Ornamental grasses provide structure and movement to a landscape, but their management in summer is often misunderstood. Unlike the severe pruning performed in late winter or early spring, trimming during the summer months is strictly a form of aesthetic maintenance. This mid-season care focuses on tidying up spent flower stalks, managing size, or removing damaged foliage rather than a major structural reduction. Understanding this distinction is the foundation for keeping these plants healthy and attractive throughout the growing season.
Identifying Grass Types and Timing
The approach to summer trimming is dictated entirely by whether a plant is a warm-season or cool-season grass. Warm-season grasses, such as Fountain Grass (Pennisetum) and Maiden Grass (Miscanthus), actively grow during the heat of summer. These grasses are robust enough to tolerate light pruning during their peak growth phase, allowing them to quickly recover from minor cosmetic cuts.
Conversely, cool-season grasses like Fescues (Festuca) and Blue Oat Grass (Helictotrichon) perform their heaviest growth in the spring and fall. They often slow down or become semi-dormant during the summer heat, making them vulnerable to stress. Cutting these grasses back hard in summer can shock the plant and lead to severe damage.
For cool-season varieties, mid-season maintenance should be limited to the gentle removal of damaged blades and dead flower stalks. If the grass looks ragged and brown, it is often best to simply clean out the dead material rather than attempting a corrective cut. Trying to force new growth by cutting back a stressed cool-season plant in the heat can irreparably harm it.
Techniques for Mid-Season Maintenance
Mid-season trimming is primarily cosmetic, aiming to maintain a clean appearance and the plant’s natural form. The most common technique is deadheading, which involves removing dried, spent flower stalks that detract from the fresh foliage. This should be done selectively by snipping the stalk near the base of the plant.
For general tidiness, especially on clump-forming varieties, target brown or damaged leaf tips. These can be removed by trimming the top third of the foliage using sharp hand shears or scissors, which allows the plant to keep its shape while removing unsightly portions. Using sharp tools prevents ragged cuts that can open the door to pests and disease.
Another technique for tidying the base is the “pull test” method for dead foliage. By wearing gloves, gently comb your fingers through the clump to pull out dry, dead blades accumulated near the crown. This action improves air circulation and prevents debris from smothering new growth. For larger warm-season grasses, you may use a hedge trimmer for a quick, uniform trim, but ensure you only take off the upper portion of the foliage to avoid an unnatural, sheared look.
Addressing Aggressive Growth or Damage
In some circumstances, a warm-season grass may need a more significant cut during the summer, known as rejuvenation pruning. This is reserved for aggressive growers like Miscanthus that have become too large or have severely “flopped” due to heavy rain or wind damage. This harder cut should only be considered in early summer, allowing maximum time for recovery before the fall.
To perform a significant cut, first use cord or bungee material to firmly tie the entire clump of grass together, simplifying the cutting process and cleanup. Using sharp hedge shears or an electric trimmer, the clump can then be cut back to a height of 6 to 12 inches from the ground. This severe reduction forces the plant to divert energy into producing a flush of new foliage.
For vigorous warm-season grasses, cutting back later than mid-July carries the risk of insufficient regrowth to insulate the crown before winter. Limiting this technique to early summer provides the plant with the longest possible period for the crown to recover.
Essential Aftercare and Preventing Harm
Proper aftercare is necessary to help the grass recover from the stress of summer trimming, particularly following a hard cut. Immediately after pruning, increased moisture is required for recovery. Apply a deep, thorough watering directly to the root zone, and maintain a regular watering schedule for several weeks to encourage vigorous new growth.
Fertilization is generally unnecessary and should be approached with caution during the summer heat. Most ornamental grasses prefer lean soil, and excessive nutrients can cause weak, floppy growth. Applying high-nitrogen fertilizer in the summer can also risk burning the foliage, as the plant is already under heat stress. If the soil is extremely poor, an application of a light, slow-release fertilizer in the spring is preferable, but avoid fertilizing the plant after a summer cut.
The greatest mistake to avoid is cutting any ornamental grass too close to the ground, or “scalping,” during the summer. Leaving a few inches of stubble, typically 4 to 6 inches, protects the crown of the plant from sun and heat damage. Cutting too low can expose the vulnerable growing point to the elements and increase the risk of moisture settling in the crown, which can lead to rot and plant loss.